The invention relates to a method for carrying out material from a pressure chamber as well as to a conveyor device for carrying out said method.
From the area of tunnel constructionxe2x80x94for example from hydro shieldsxe2x80x94it is known to carry out muck (excavation), which has been stripped in-situ in the stripping chamber, out of the stripping chamber through pipe conduits with the help of the liquid supporting the working face and to haul it away by pumps. This method suffers from the drawback that along with the muck huge amounts of liquid have to be transported and separated thereafter from the muck. The supporting liquid is recuperated. This calls for large separation plants. The soil extracted by the separation process still contains a high content of support liquid and is unfit for short-term soil-mechanical processing. This soil causes further costs for its shipping away and dumping. The disposal of the stripped muck and the support liquid comprised therein is thus very costly with shields working with supporting the working face by a liquid.
With EPB-shields (EPB=Earth Pressure Balanced) stripped soil, which is adequately impermeable by nature and conditioned by suitable agents, such as foams, is used for supporting the working face. So far, this soil has been transported away from the stripping chamber by screw conveyors.
The compacted column of soil in the screw conveyor during the conveying process acts as a seal against the pressure in the stripping chamber and as a lock to the unpressurized rear shield space. The larger the permeability of the soil the larger has to be the length of the sealing column of soil and correspondingly the screw of the conveyor. The effectiveness of the stopper formed by the soil as a pressure seal for the chamber has its limits at a soil with a k-value greater than 10xe2x88x925 m/s and at a support pressure above about 2 bar.
Soils with too great a permeability can no longer withstand the pore pressure in the soil stopper, thus making necessary a lock for material arranged at the end of the screw conveyor. Such locks for material are in a wider sense pumps, such as piston pumps, hose pumps and centrifugal pumps, as well as drawer-like and rotating lift-locks. They comprise rotating and moving parts which are subject to high wear. They normally require a system-related conditioning of the muck to be carried out which contradicts the object of achieving an extract as dry as possible. Their extraction capacity in relation to the hauling capacity of the shield is small. To increase the extraction capacity large constructions are necessary which can be accommodated in the shield space only at large tunnel cross-sections. This means that the yield capacity of the shield can not fully be utilized. Therefore, such excavation equipment considerably reduces the economy of a heading machine.
From DE-A-36 272 70 an EPB-shield is known where the loosened soil is transported out of the stripping chamber with a screw conveyor. The screw of the conveyor presses the stripped soil out of the pressure chamber towards a closable sliding valve outlet in the inner space of the shield, and from said outlet of the sliding valve the soil is carried away on a conveyor belt arranged below said outlet in the area of atmospheric pressure. As explained above, such a conveyor plant is unable to hold back the higher pressure in the pressure chamber if the soil is permeable. With permeable soils the sliding valve has to be closed and the excavation of soil has to be stopped.
The invention aims at developing a method and a device for carrying out material from a pressure chamber which also allow the excavation of soils with a permeability k greater than 10xe2x88x925 m/s in a simple, wear-proof, space-saving and reliable manner.
According to the method the excavation of muck from a pressure chamber is achieved by using, in a surprisingly simple manner, the energy stored in a compressed mediumxe2x80x94such as a gas, a gas mixture, foam or foamed suspensionxe2x80x94in the pores in the muck at the moment of depressurisation. This method is preferably developed for tunnel construction. The same method could be used in analogue manner in other industries, where muck-like substances are to be carried out of pressurized containers, for example in primary matter industries, the chemical industry, garbage dressing and garbage disposal.
The method according to the invention is principally independent of a conveyor device, such as a pump or a screw conveyor, connected in front of the conveyor chamber. The conveyor chamber is a simple cell which only serves to form a closable space, and it comprises no rotating parts or mechanical drives. Thus, the conveyor chamber is very insensitive under operation. It requires little space and may accommodated in the shield space in a simple manner.
The times needed for charging and discharging the conveyor chamber are short, thus enabling a fast cycle sequence and a large throughput. Thus, the conveyor device according to the invention is most adapted to satisfy the excavation demands of a shield heading machine.
The material to be carried out may be conditioned with very little water, thus yielding favourable conditions for an economic excavation and simple re-storage.
In tunnel construction often varying layers of different kinds of soil have to be excavated, which can not homogenously be mixed or conditioned. When inhomogenous mixtures of pore-poor, largely impervious soils and highly gas and water pervious soils have to be excavated under holding the pressure, it may occur that the change of the kinds of soil during excavation results in a situation where the muck to be excavated exhibits such a small porosity that the expansion energy stored in the muck is not sufficient to bring about a complete and sufficiently fast extraction. This tendency is enhanced by a moderate pressure gradient.
In order to enable a reliable use of the method suggested also under these conditions an accumulator for pressurized gas is alternatively arranged at the inlet area of the conveyor chamber which, if necessary, provides additionally required expansion energy and which may become connected if inhomogenious soil mixtures of different cohesion or soils with a small expansion energy have to be excavated.